Patterning process and resist composition

ABSTRACT

A negative pattern is formed by coating a resist composition comprising a polymer comprising recurring units of acid labile group-substituted vinyl alcohol and maleic anhydride and/or maleimide, an acid generator, and an organic solvent onto a substrate, prebaking, exposing to high-energy radiation, and developing in an organic solvent developer such that the unexposed region of resist film is dissolved away and the exposed region of resist film is not dissolved. In image formation via positive/negative reversal by organic solvent development, the resist film is characterized by a high dissolution contrast between the unexposed and exposed regions.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2011-202930 filed in Japan on Sep. 16, 2011,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a pattern forming process involving exposureof resist film, deprotection reaction with the aid of acid and heat, anddevelopment in an organic solvent to form a negative tone pattern inwhich the unexposed region is dissolved and the exposed region is notdissolved. It also relates to a resist composition used therein.

BACKGROUND ART

In the recent drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. Thephotolithography which is currently on widespread use in the art isapproaching the essential limit of resolution determined by thewavelength of a light source. As the light source used in thelithography for resist pattern formation, g-line (436 nm) or i-line (365nm) from a mercury lamp was widely used in 1980's. Reducing thewavelength of exposure light was believed effective as the means forfurther reducing the feature size. For the mass production process of 64MB dynamic random access memories (DRAM, processing feature size 0.25 μmor less) in 1990's and later ones, the exposure light source of i-line(365 nm) was replaced by a KrF excimer laser having a shorter wavelengthof 248 nm. However, for the fabrication of DRAM with a degree ofintegration of 256 MB and 1 GB or more requiring a finer patterningtechnology (processing feature size 0.2 μm or less), a shorterwavelength light source was required. Over a decade, photolithographyusing ArF excimer laser light (193 nm) has been under activeinvestigation. It was expected at the initial that the ArF lithographywould be applied to the fabrication of 180-nm node devices. However, theKrF excimer lithography survived to the mass-scale fabrication of 130-nmnode devices. So, the full application of ArF lithography started fromthe 90-nm node. The ArF lithography combined with a lens having anincreased numerical aperture (NA) of 0.9 is considered to comply with65-nm node devices. For the next 45-nm node devices which required anadvancement to reduce the wavelength of exposure light, the F₂lithography of 157 nm wavelength became a candidate. However, for thereasons that the projection lens uses a large amount of expensive CaF₂single crystal, the scanner thus becomes expensive, hard pellicles areintroduced due to the extremely low durability of soft pellicles, theoptical system must be accordingly altered, and the etch resistance ofresist is low; the development of F₂ lithography was stopped andinstead, the ArF immersion lithography was introduced.

In the ArF immersion lithography, the space between the projection lensand the wafer is filled with water having a refractive index of 1.44.The partial fill system is compliant with high-speed scanning and whencombined with a lens having a NA of 1.3, enables mass production of45-nm node devices.

One candidate for the 32-nm node lithography is lithography usingextreme ultraviolet (EUV) radiation with wavelength 13.5 nm. The EUVlithography has many accumulative problems to be overcome, includingincreased laser output, increased sensitivity, increased resolution andminimized edge roughness of resist film, defect-free MoSi laminate mask,reduced aberration of reflection mirror, and the like.

Another candidate for the 32-nm node lithography is high refractiveindex liquid immersion lithography. The development of this technologywas stopped because LUAG, a high refractive index lens candidate had alow transmittance and the refractive index of liquid did not reach thegoal of 1.8.

The process that now draws attention under the above-discussedcircumstances is a double patterning process involving a first set ofexposure and development to form a first pattern and a second set ofexposure and development to form a pattern between the first patternfeatures. A number of double patterning processes are proposed. Oneexemplary process involves a first set of exposure and development toform a photoresist pattern having lines and spaces at intervals of 1:3,processing the underlying layer of hard mask by dry etching, applyinganother layer of hard mask thereon, a second set of exposure anddevelopment of a photoresist film to form a line pattern in the spacesof the first exposure, and processing the hard mask by dry etching,thereby forming a line-and-space pattern at a half pitch of the firstpattern. An alternative process involves a first set of exposure anddevelopment to form a photoresist pattern having spaces and lines atintervals of 1:3, processing the underlying layer of hard mask by dryetching, applying a photoresist layer thereon, a second set of exposureand development to form a second space pattern on the remaining hardmask portion, and processing the hard mask by dry etching. In eitherprocess, the hard mask is processed by two dry etchings.

As compared with the line pattern, the hole pattern is difficult toreduce the feature size. In order for the prior art method to form fineholes, an attempt is made to form fine holes by under-exposure of apositive resist film combined with a hole pattern mask. This, however,results in the exposure margin being extremely narrowed. It is thenproposed to form holes of greater size, followed by thermal flow orRELACS® method to shrink the holes as developed. However, there is aproblem that control accuracy becomes lower as the pattern size afterdevelopment and the size after shrinkage differ greater and the quantityof shrinkage is greater. With the hole shrinking method, the hole sizecan be shrunk, but the pitch cannot be narrowed.

It is then proposed in Non-Patent Document 1 that a pattern ofX-direction lines is formed in a positive resist film using dipoleillumination, the resist pattern is cured, another resist material iscoated thereon, and a pattern of Y-direction lines is formed in theother resist film using dipole illumination, leaving a grid linepattern, spaces of which provide a hole pattern. Although a hole patterncan be formed at a wide margin by combining X and Y lines and usingdipole illumination featuring a high contrast, it is difficult to etchvertically staged line patterns at a high dimensional accuracy. It isproposed in Non-Patent Document 2 to form a hole pattern by exposure ofa negative resist film through a Levenson phase shift mask ofX-direction lines combined with a Levenson phase shift mask ofY-direction lines. However, the crosslinking negative resist film hasthe drawback that the resolving power is low as compared with thepositive resist film, because the maximum resolution of ultrafine holesis determined by the bridge margin.

A hole pattern resulting from a combination of two exposures of X- andY-direction lines and subsequent image reversal into a negative patterncan be formed using a high-contrast line pattern of light. Thus holeshaving a narrow pitch and fine size can be opened as compared with theprior art.

Non-Patent Document 3 reports three methods for forming hole patternsvia image reversal. The three methods are: method (1) involvingsubjecting a positive resist composition to two double-dipole exposuresof X and Y lines to form a dot pattern, depositing a SiO₂ film thereonby LPCVD, and effecting O₂—RIE for reversal of dots into holes; method(2) involving forming a dot pattern by the same steps as in (1), butusing a resist composition designed to turn alkali-soluble andsolvent-insoluble upon heating, coating a phenol-base overcoat filmthereon, effecting alkaline development for image reversal to form ahole pattern; and method (3) involving double dipole exposure of apositive resist composition and organic solvent development for imagereversal to form holes.

The organic solvent development to form a negative pattern is atraditional technique. A resist composition comprising cyclized rubberis developed using an alkene such as xylene as the developer. An earlychemically amplified resist composition comprisingpoly(tert-butoxycarbonyloxystyrene) is developed with anisole as thedeveloper to form a negative pattern.

Recently a highlight is put on the organic solvent development again. Itwould be desirable if a very fine hole pattern, which is not achievablewith the positive tone, is resolvable through negative tone exposure. Tothis end, a positive resist composition featuring a high resolution issubjected to organic solvent development to form a negative pattern. Anattempt to double a resolution by combining two developments, alkalinedevelopment and organic solvent development is under study.

As the ArF resist composition for negative tone development with organicsolvent, positive ArF resist compositions of the prior art design may beused. Such pattern forming processes are described in Patent Documents 1to 3. These patent documents disclose resist compositions for organicsolvent development comprising a copolymer of hydroxyadamantanemethacrylate, a copolymer of norbornane lactone methacrylate, and acopolymer of methacrylate having acidic groups including carboxyl,sulfo, phenol and thiol groups substituted with two or more acid labilegroups, and pattern forming processes using the same.

Further, Patent Document 4 discloses a process for forming a patternthrough organic solvent development in which a protective film isapplied onto a resist film. Patent Document 5 discloses a topcoatlessprocess for forming a pattern through organic solvent development inwhich an additive is added to a resist composition so that the additivemay segregate at the resist film surface after spin coating to providethe surface with improved water repellency.

In these patent documents, negative patterns are formed by usingconventional resist compositions and developing them in organicsolvents. The contrast of organic solvent development is not so high.For contrast enhancement, it is required to have a resist compositiondesigned especially for organic solvent development.

CITATION LIST

-   Patent Document 1: JP-A 2008-281974-   Patent Document 2: JP-A 2008-281975-   Patent Document 3: JP 4554665-   Patent Document 4: JP 4590431-   Patent Document 5: JP-A 2008-309879-   Non-Patent Document 1: Proc. SPIE Vol. 5377, p. 255 (2004)-   Non-Patent Document 2: IEEE IEDM Tech. Digest 61 (1996)-   Non-Patent Document 3: Proc. SPIE Vol. 7274, p. 72740N (2009)

DISCLOSURE OF INVENTION

The organic solvent development is low in dissolution contrast, ascompared with the positive resist system adapted to be dissolved inalkaline developer when deprotection reaction takes place to produceacidic carboxyl groups. Specifically, in the case of alkaline developer,the alkali dissolution rate differs more than 1,000 times betweenunexposed and exposed regions, whereas the difference is only about 10times in the case of organic solvent development. In the case ofalkaline water development, the dissolution rate is improved byneutralization reaction with carboxyl groups. In the case of organicsolvent development with no accompanying reaction, the dissolution rateis low because dissolution is solely due to solvation. It is necessarynot only to improve the dissolution rate of the unexposed region, butalso to reduce the dissolution rate of the exposed region that is aremaining portion of resist film. If the dissolution rate of the exposedregion is high, the thickness of the remaining film is so reduced thatthe underlying substrate may not be processed by etching through thepattern as developed. Further it is important to enhance the gradient orgamma (γ) at the dose corresponding to dissolution/non-dissolutionconversion. A low γ value is prone to form an inversely tapered profileand allows for pattern collapse in the case of a line pattern. To obtaina perpendicular pattern, the resist must have a dissolution contrasthaving a γ value as high as possible.

While prior art photoresist compositions of the alkaline aqueoussolution development type are described in Patent Documents 1 to 3, theyhave a low dissolution contrast upon organic solvent development. Itwould be desirable to have a novel material having a significantdifference in dissolution rate between the exposed and unexposed regionsand capable of achieving a high dissolution contrast (γ) upon organicsolvent development.

When an attempt is made to form a hole pattern through negativedevelopment, regions surrounding the holes receive light so that excessacid is generated therein. Since the holes are not opened if the aciddiffuses inside the holes, control of acid diffusion is also important.

An object of the invention is to provide a negative pattern-formingresist composition which has a significant dissolution contrast and ahigh sensitivity upon organic solvent development. Another object is toprovide a pattern forming process capable of forming a hole pattern viapositive/negative reversal by organic solvent development.

The inventors have found that a polymer comprising recurring units ofacid labile group-substituted vinyl alcohol and maleic anhydride and/ormaleimide is effective, that a resist composition comprising the polymeris improved in dissolution contrast upon organic solvent development,and that the hole pattern resulting from positive/negative reversal isimproved in sensitivity, dimensional uniformity, and pattern profile.

Accordingly, in one aspect, the invention provides a pattern formingprocess comprising the steps of applying a resist composition onto asubstrate, the resist composition comprising a polymer comprisingrecurring units of acid labile group-substituted vinyl alcohol andmaleic anhydride and/or maleimide, an acid generator, and an organicsolvent; prebaking the composition to form a resist film; exposing theresist film to high-energy radiation; baking; and developing the exposedfilm in an organic solvent-based developer to form a negative patternwherein the unexposed region of film is dissolved away and the exposedregion of film is not dissolved.

In a preferred embodiment, the recurring units of acid labilegroup-substituted vinyl alcohol and the recurring units of maleicanhydride and/or maleimide are represented by the general formula (1).

Herein R¹ is an acid labile group, X is an oxygen atom or NR², R² ishydrogen, hydroxyl, or a straight, branched or cyclic C₁-C₆ alkyl groupwhich may contain one or two or more groups selected from the groupconsisting of hydroxyl, ether, ester, carbonyl, and acid-labile groups,a1 and a2 are numbers in the range: 0<a1<1.0, 0<a2<1.0, and 0<a1+a2≦1.0.

Another embodiment is a pattern forming process comprising the steps ofapplying a resist composition onto a substrate, the resist compositioncomprising a polymer comprising recurring units of acid labilegroup-substituted vinyl alcohol and maleic anhydride and/or maleimide asrepresented by formula (1), an acid generator, and an organic solvent;prebaking the composition to form a resist film; forming a protectivefilm on the resist film; exposing the resist film to high-energyradiation; baking; and applying an organic solvent-based developer todissolve away the protective film and the unexposed region of resistfilm for forming a negative pattern wherein the exposed region of resistfilm is not dissolved.

In a preferred embodiment, the acid generator comprises both an acidgenerator capable of generating a sulfonic acid fluorinated atalpha-position, imide acid or methide acid, and a sulfonate of asulfonic acid non-fluorinated at alpha-position or an optionallyfluorinated carboxylic acid.

In a preferred embodiment, the developer comprises at least one organicsolvent selected from the group consisting of 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,amyl acetate, isoamyl acetate, butenyl acetate, phenyl acetate, propylformate, butyl formate, isobutyl formate, amyl formate, isoamyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,amyl lactate, isoamyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, benzyl acetate,methyl phenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate.

In a preferred embodiment, the step of exposing the resist film tohigh-energy radiation includes ArF excimer laser lithography of 193 nmwavelength, EUV lithography of 13.5 nm wavelength or EB lithography.

Preferably, the ArF lithography of 193 nm wavelength uses a halftonephase shift mask bearing a dot shifter pattern, whereby a pattern ofholes is formed at the dots after development.

Preferably, the exposure step uses halftone phase shift masks andincludes two exposures of two intersecting sets of lines, whereby apattern of holes is formed at the intersections between lines afterdevelopment.

Also preferably, the exposure step uses a halftone phase shift maskbearing lattice-like shifter gratings, whereby a pattern of holes isformed at the intersections of gratings after development.

In a preferred embodiment, a copolymer obtained by further incorporatingrecurring units of at least one type selected from sulfonium salts (e1)to (e3) of the following general formula into the polymer is usedinstead of the acid generator.

Herein R²⁰, R²⁴ and R²⁸ each are hydrogen or methyl, R²¹ is a singlebond, phenylene, —O—R³³—, or —C(═O)—Y—R³³—, Y is oxygen or NH, R³³ is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl (—CO—), ester (—COO—),ether (—O—) or hydroxyl radical, R²², R²³, R²⁵, R²⁶, R²⁷, R²⁹, R³⁰, andR³¹ are each independently a straight, branched or cyclic C₁-C₁₂ alkylgroup which may contain a carbonyl, ester or ether radical, or a C₆-C₁₂aryl, C₇-C₂₀ aralkyl, or thiophenyl group, Z₀ is a single bond,methylene, ethylene, phenylene, fluorophenylene, —O—R³²—, or—C(═O)—Z₁—R³²—, Z₁ is oxygen or NH, R³² is a straight, branched orcyclic C₁-C₆ alkylene group, alkenylene group or phenylene group, whichmay contain a carbonyl, ester, ether or hydroxyl radical, M⁻ is anon-nucleophilic counter ion, e1, e2 and e3 are numbers in the range:0≦e1≦0.3, 0≦e2≦0.3, 0≦e≦0.3, and 0<e1+e2+e3≦0.3.

In another aspect, the invention provides a negative pattern-formingresist composition comprising a polymer comprising recurring units (a1)of acid labile group-substituted vinyl alcohol and recurring units (a2)of maleic anhydride and/or maleimide, represented by formula (1), anacid generator, and an organic solvent. The polymer is dissolvable in adeveloper selected from the group consisting of 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,amyl acetate, isoamyl acetate, butenyl acetate, phenyl acetate, propylformate, butyl formate, isobutyl formate, amyl formate, isoamyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,amyl lactate, isoamyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, benzyl acetate,methyl phenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate.

In a preferred embodiment of the resist composition, the polymer furthercomprises recurring units of at least one type selected from sulfoniumsalts (e1) to (e3) of the above general formula in copolymerized form.On use of this copolymer, the acid generator is omitted.

Preferably, the acid generator comprises both an acid generator capableof generating a sulfonic acid fluorinated at alpha-position, imide acidor methide acid, and a sulfonate of a sulfonic acid non-fluorinated atalpha-position or an optionally fluorinated carboxylic acid.

Advantageous Effects of Invention

An image is formed via positive/negative reversal on organic solventdevelopment using a photoresist film formed of a resist compositioncomprising a polymer comprising recurring units of acid labilegroup-substituted vinyl alcohol and maleic anhydride and/or maleimideand an acid generator. The resist film is characterized by a highdissolution contrast between the unexposed region of promoteddissolution and the exposed region of inhibited dissolution. When theresist film is exposed to radiation and developed in an organic solvent,a fine hole pattern with a controlled size and high sensitivity can beformed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a patterning process according oneembodiment of the invention. FIG. 1A shows a photoresist film disposedon a substrate, FIG. 1B shows the resist film being exposed, and FIG. 1Cshows the resist film being developed in an organic solvent.

FIG. 2 is an optical image of X-direction lines having a pitch of 90 nmand a line size of 45 nm printed under conditions: ArF excimer laser ofwavelength 193 nm, NA 1.3 lens, dipole illumination, 6% halftone phaseshift mask, and s-polarization.

FIG. 3 is an optical image of Y-direction lines like FIG. 2.

FIG. 4 shows a contrast image obtained by overlaying the optical imageof X-direction lines in FIG. 2 with the optical image of Y-directionlines in FIG. 3.

FIG. 5 illustrates a mask bearing a lattice-like pattern.

FIG. 6 is an optical image of a lattice-like line pattern having a pitchof 90 nm and a line width of 30 nm printed under conditions: NA 1.3lens, cross-pole illumination, 6% halftone phase shift mask, andazimuthally polarized illumination.

FIG. 7 illustrates a mask bearing a dot pattern of square dots having apitch of 90 nm and a side width of 55 nm.

FIG. 8 is an optical image resulting from the mask of FIG. 7, printedunder conditions: NA 1.3 lens, cross-pole illumination, 6% halftonephase shift mask, and azimuthally polarized illumination, showing itscontrast.

FIG. 9 illustrates a mask bearing a lattice-like pattern having a pitchof 90 nm and a line width of 20 nm on which thick crisscross orintersecting line segments are disposed where dots are to be formed.

FIG. 10 is an optical image resulting from the mask of FIG. 9, showingits contrast.

FIG. 11 illustrates a mask bearing a lattice-like pattern having a pitchof 90 nm and a line width of 15 nm on which thick dots are disposedwhere dots are to be formed.

FIG. 12 is an optical image resulting from the mask of FIG. 11, showingits contrast.

FIG. 13 illustrates a mask without a lattice-like pattern.

FIG. 14 is an optical image resulting from the mask of FIG. 13, showingits contrast.

FIG. 15 is a diagram showing film thickness versus exposure dose inExample 1-1.

FIG. 16 is a diagram showing film thickness versus exposure dose inComparative Example 1-1.

FIG. 17 illustrates a lattice-like mask used in ArF lithographypatterning test 2.

FIG. 18 illustrates an aperture configuration in an exposure tool ofdipole illumination for enhancing the contrast of X-direction lines.

FIG. 19 illustrates an aperture configuration in an exposure tool ofdipole illumination for enhancing the contrast of Y-direction lines.

FIG. 20 illustrates an aperture configuration in an exposure tool ofcross-pole illumination for enhancing the contrast of both X andY-direction lines.

DESCRIPTION OF EMBODIMENTS

The terms “a” and “an” herein do not denote a limitation of quantity,but rather denote the presence of at least one of the referenced item.“Optional” or “optionally” means that the subsequently described eventor circumstances may or may not occur, and that description includesinstances where the event or circumstance occurs and instances where itdoes not. As used herein, the notation (C_(n)-C_(m)) means a groupcontaining from n to m carbon atoms per group. As used herein, the term“film” is used interchangeably with “coating” or “layer.” The term“processable layer” is interchangeable with patternable layer and refersto a layer that can be processed such as by etching to form a patterntherein.

The abbreviations and acronyms have the following meaning.

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

Briefly stated, the invention pertains to a pattern forming processutilizing positive/negative reversal and comprising the steps ofapplying a resist composition comprising a polymer comprising recurringunits of vinyl alcohol in which the hydrogen of hydroxyl group issubstituted by an acid labile group and recurring units of maleicanhydride and/or maleimide, an acid generator, and an organic solventonto a substrate, prebaking to remove the unnecessary solvent and form aresist film, exposing to high-energy radiation, PEB, and developing inan organic solvent developer to form a negative pattern.

In general, a polymer having hydroxyl group is more hydrophilic and lesssoluble in organic solvents than a polymer having carboxyl group. Ascompared with the polymer capable of generating carboxyl group viaacid-catalyzed elimination reaction, the polymer capable of generatinghydroxyl group has a low solubility in organic solvent afterdeprotection and thus forms a pattern of thicker remaining film. Thepolymer capable of generating hydroxyl group becomes insoluble in thedeveloper even after a less extent of deprotection, and thus provides ahigher sensitivity and a higher gradient (γ) of dissolution than thepolymer having a carboxyl group substituted with an acid labile group.This renders the pattern as developed more perpendicular and expands themargin of focus and exposure dose. Although a copolymer of vinyl alcoholwith maleic anhydride or maleimide is highly hydrophilic, it is leastalkali soluble. Thus the copolymer fails to form a positive pattern viaalkaline development. Thus no or little studies have been made on suchcopolymers. The inventors have found that the hydroxyl group on suchcopolymers is an optimum umpolung (or polarity-conversion) group in thecase of organic solvent development,

While the polymer is defined as comprising recurring units of acidlabile group-substituted vinyl alcohol and maleic anhydride and/ormaleimide, recurring units (a1) and (a2) represented by the generalformula (1) are preferred.

Herein R¹ is an acid labile group, X is an oxygen atom or NR², R² ishydrogen, hydroxyl, or a straight, branched or cyclic C₁-C₆ alkyl groupwhich may contain one or two or more groups selected from the groupconsisting of hydroxyl, ether, ester, carbonyl, and acid-labile groups,molar fractions a1 and a2 are in the range: 0<a1<1.0, 0<a2<1.0, and0<a1+a2≦1.0.

Suitable monomers from which recurring units (a1) are derived includevinyl ethers which are acid labile group-substituted vinyl alcohols.Suitable monomers from which recurring units (a2) are derived includemaleic anhydride and maleimides which are exemplified below.

While it is essential to use a polymer comprising recurring units (a1)of acid labile group-substituted vinyl alcohol and recurring units (a2)of maleic anhydride and/or maleimide as the base resin in the resistcomposition which is used in the pattern forming process of theinvention, the polymer may have further copolymerized therein recurringunits (b) having a hydroxyl group substituted with an acid labile group(other than vinyl alcohol). Examples of the monomer having a hydroxylgroup substituted with an acid labile group (other than vinyl alcohol)are shown below. Herein R³ is hydrogen or methyl, and R⁴ is an acidlabile group.

In addition to the recurring units (a1), (a2) and (b), recurring units(c) having a carboxyl group substituted with an acid labile group asshown below may also be copolymerized.

Herein R⁵ is hydrogen or methyl. R⁶ is an acid labile group. Z is asingle bond, phenylene, naphthylene, or —C(═O)—O—R⁷— wherein R⁷ is astraight, branched or cyclic C₁-C₁₀ alkylene group which may contain anether radical, ester radical, lactone ring or hydroxyl radical, or aphenylene or naphthylene group.

Suitable monomers Mc from which the recurring units (c) are derived havethe following formula wherein R⁵, R⁶ and Z are as defined above.

Examples of the monomer Mc wherein Z is a different group are givenbelow.

R¹ and R² in formula (1), R⁴ and R⁶ in units (b) and (c) are acid labilegroups while they may be the same or different. The acid labile groupmay be selected from a variety of such groups, specifically groups ofthe formula (AL-10), acetal groups of the formula (AL-11), tertiaryalkyl groups of the formula (AL-12), and oxoalkyl groups of 4 to 20carbon atoms, but not limited thereto.

In formulae (AL-10) and (AL-11), R⁵¹ and R⁵⁴ each are a monovalenthydrocarbon group, typically straight, branched or cyclic alkyl group,of 1 to 40 carbon atoms, more specifically 1 to 20 carbon atoms, whichmay contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine.R⁵² and R⁵³ each are hydrogen or a monovalent hydrocarbon group,typically straight, branched or cyclic alkyl group, of 1 to 20 carbonatoms which may contain a heteroatom such as oxygen, sulfur, nitrogen orfluorine. The subscript “a5” is an integer of 0 to 10, and especially 1to 5. Alternatively, a pair of R⁵² and R⁵³, R⁵² and R⁵⁴, or R⁵³ and R⁵⁴may bond together to form a ring, specifically aliphatic ring, with thecarbon atom or the carbon and oxygen atoms to which they are attached,the ring having 3 to 20 carbon atoms, especially 4 to 16 carbon atoms.

In formula (AL-12), R⁵⁵, R⁵⁶ and R⁵⁷ each are a monovalent hydrocarbongroup, typically straight, branched or cyclic alkyl group, of 1 to 20carbon atoms which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine. Alternatively, a pair of R⁵⁵ and R⁵⁶, R⁵⁵ and R⁵⁷,or R⁵⁶ and R⁵⁷ may bond together to form a ring, specifically aliphaticring, with the carbon atom to which they are attached, the ring having 3to 20 carbon atoms, especially 4 to 16 carbon atoms.

Illustrative examples of the group of formula (AL-10) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl and2-tetrahydrofuranyloxycarbonylmethyl as well as substituent groups ofthe following formulae (AL-10)-1 to (AL-10)-10.

In formulae (AL-10)-1 to (AL-10)-10, R⁵⁸ is each independently astraight, branched or cyclic C₁-C₈ alkyl group, C₆-C₂₀ aryl group orC₇-C₂₀ aralkyl group; R⁵⁹ is hydrogen or a straight, branched or cyclicC₁-C₂₀ alkyl group; R⁶⁰ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group;and a5 is an integer of 0 to 10, especially 1 to 5.

Illustrative examples of the acetal group of formula (AL-11) includethose of the following formulae (AL-11)-1 to (AL-11)-112.

Other examples of acid labile groups include those of the followingformula (AL-11a) or (AL-11b) while the polymer may be crosslinked withinthe molecule or between molecules with these acid labile groups.

Herein R⁶¹ and R⁶² each are hydrogen or a straight, branched or cyclicC₁-C₈ alkyl group, or R⁶¹ and R⁶² may bond together to form a ring withthe carbon atom to which they are attached, and R⁶¹ and R⁶² are straightor branched C₁-C₈ alkylene groups when they form a ring. R⁶³ is astraight, branched or cyclic C₁-C₁₀ alkylene group. Each of b5 and d5 is0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and c5is an integer of 1 to 7. “A” is a (c5+1)-valent aliphatic or alicyclicsaturated hydrocarbon group, aromatic hydrocarbon group or heterocyclicgroup having 1 to 50 carbon atoms, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,carbonyl radicals or fluorine atoms. “B” is —CO—O—, —NHCO—O— or—NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkanetriyl and alkanetetraylgroups, and C₆-C₃₀ arylene groups, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,acyl radicals or halogen atoms. The subscript c5 is preferably aninteger of 1 to 3.

The crosslinking acetal groups of formulae (AL-11a) and (AL-11b) areexemplified by the following formulae (AL-11)-113 through (AL-11)-120.

Illustrative examples of the tertiary alkyl group of formula (AL-12)include tert-butyl, triethylcarbyl, 1-ethylnorbornyl,1-methylcyclohexyl, 1-ethylcyclopentyl, and tert-amyl groups as well asthose of (AL-12)-1 to (AL-12)-16.

Herein R⁶⁴ is each independently a straight, branched or cyclic C₁-C₈alkyl group, C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group, or two R⁶⁴groups may bond together to form a ring with the carbon atom to whichthey are attached, the ring being of 3 to 20 carbon atoms, specifically4 to 16 carbon atoms, typically aliphatic ring; R⁶⁵ and R⁶⁷ each arehydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group; and R⁶⁶is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group.

With acid labile groups containing R⁶⁸ representative of a di- orpoly-valent alkylene or arylene group as shown by formula (AL-12)-17,the polymer may be crosslinked within the molecule or between molecules.In formula (AL-12)-17, R⁶⁴ is as defined above, R⁶⁸ is a single bond, astraight, branched or cyclic C₁-C₂₀ alkylene group or arylene group,which may contain a heteroatom such as oxygen, sulfur or nitrogen, andb6 is an integer of 0 to 3. It is noted that formula (AL-12)-17 isapplicable to all acid labile groups R¹, R², R⁴, and R⁶.

The groups represented by R⁶⁴, R⁶⁵, R⁶⁶ and R⁶⁷ may contain a heteroatomsuch as oxygen, nitrogen or sulfur. Such groups are exemplified by thoseof the following formulae (AL-13)-1 to (AL-13)-7.

While the polymer used as the base resin in the resist compositioncomprises essentially recurring units (a1) and (a2) having formula (1)and optionally (and preferably) recurring units (b) or (c) having anacid labile group, it may have further copolymerized therein recurringunits (d) derived from monomers having adhesive groups such as hydroxy,cyano, carbonyl, ester, ether groups, lactone rings, carboxyl,carboxylic anhydride, sulfonic acid ester, disulfone or carbonategroups. Of these, recurring units having lactone ring as the adhesivegroup are most preferred.

Examples of suitable monomers from which recurring units (d) are derivedare given below.

In a preferred embodiment, the polymer has further copolymerized thereinunits selected from sulfonium salts (e1) to (e3) represented by thegeneral formulae below. Understandably, when the sulfonium salt unitsare incorporated in the polymer, the addition of an acid generator tothe resist composition may be omitted.

Herein R²⁰, R²⁴ and R²⁸ each are hydrogen or methyl. R²¹ is a singlebond, phenylene, —O—R³³—, or —C(═O)—Y—R³³— wherein Y is oxygen or NH,and R³³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene group or phenylene group, which may contain a carbonyl(—CO—), ester (—COO—), ether (—O—) or hydroxyl radical. R²², R²³, R²⁵,R²⁶, R²⁷, R²⁹, R³⁰, and R³¹ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether radical, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group. Z₀is a single bond, methylene, ethylene, phenylene, fluorophenylene,—O—R³²—, or —C(═O)—Z₁—R³²— wherein Z₁ is oxygen or NH, and R³² is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl, ester, ether or hydroxylradical. M⁻ is a non-nucleophilic counter ion. The subscripts e1, e2 ande3 are in the range: 0≦e1≦0.3, 0≦e2≦0.3, 0≦e3≦0.3, and 0≦e1+e2+e3≦0.3.

Besides the recurring units described above, the polymer may havefurther copolymerized therein additional recurring units, for example,recurring units (f) having a non-leaving hydrocarbon group as describedin JP-A 2008-281980. Examples of the non-leaving hydrocarbon group otherthan those described in JP-A 2008-281980 include indene, acenaphthylene,and norbornadiene derivatives. Copolymerization of recurring units (f)having a non-leaving hydrocarbon group facilitates dissolution of thepolymer in organic solvent-based developer.

It is also possible to incorporate recurring units (g) having an oxiraneor oxetane ring into the polymer. Where recurring units (g) having anoxirane or oxetane ring are copolymerized in the polymer, the exposedregion of resist film will be crosslinked, leading to improvements infilm retention of the exposed region and etch resistance. Examples ofthe recurring units (g) having an oxirane or oxetane ring are givenbelow wherein R⁸ is hydrogen or methyl.

The subscripts a1, a2, b, c, d, e1, e2, e3, f, and g indicative ofproportions of corresponding recurring units are in the range: 0<a1<1.0,0<a2<1.0, 0<a1+a2≦1.0, 0≦b<1.0, 0≦c<1.0, 0≦d<1.0, 0≦e1≦0.3, 0≦e2≦0.3,0≦e3≦0.3, 0≦e1+e2+e3≦0.3, 0≦f<0.4, and 0≦g<0.6;

preferably 0.1≦a1≦0.9, 0.1≦a2≦0.9, 0.1≦a1+a2≦0.9, 0≦b≦0.9, 0≦c≦0.9,0.1≦d≦0.9, 0≦e1≦0.18, 0≦e2≦0.18, 0≦e3≦0.18, 0≦e1+e2+e3<0.18, 0≦f≦0.3,and 0≦g≦0.5, provided that a1+a2+b+c+d+e1+e2+e3+f+g=1.

The polymer serving as the base resin in the resist composition used inthe pattern forming process of the invention should preferably have aweight average molecular weight (Mw) in the range of 1,000 to 500,000,and more preferably 2,000 to 30,000, as measured by GPC versuspolystyrene standards using tetrahydrofuran solvent. With too low a Mw,a film thickness loss is likely to occur upon organic solventdevelopment. A polymer with too high a Mw may lose solubility in organicsolvent and have a likelihood of footing after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that followingexposure, foreign matter is left on the pattern or the pattern profileis exacerbated. The influences of molecular weight and dispersity becomestronger as the pattern rule becomes finer. Therefore, themulti-component copolymer should preferably have a narrow dispersity(Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide aresist composition suitable for micropatterning to a small feature size.

The polymer used herein may be synthesized by any desired method, forexample, by dissolving unsaturated bond-containing monomerscorresponding to the respective units (a1), (a2), (b), (c), (d), (e1),(e2), (e3), (f), and (g) in an organic solvent, adding a radicalinitiator thereto, and effecting heat polymerization. Examples of theorganic solvent which can be used for polymerization include toluene,benzene, tetrahydrofuran, diethyl ether and dioxane. Examples of thepolymerization initiator used herein include 2,2′-azobisisobutyronitrile(AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours. The acid labile group that has been incorporated in the monomermay be kept as such, or the product may be protected or partiallyprotected after polymerization.

It is acceptable to use a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity as well as a blendof an inventive polymer and another polymer free of units of acid labilegroup-substituted vinyl alcohol, maleic anhydride and maleimide or ablend of an inventive polymer and a polymer comprising recurring unitshaving an acid labile group-substituted hydroxyl group other than theacid labile group-substituted vinyl alcohol (i.e., units (a1) and (a2))or an acid labile group-substituted carboxyl group, for example, apolymer comprising recurring units (b) and/or (c).

In a further embodiment, the inventive polymer may be blended with apolymer of the conventional type wherein the exposed region is dissolvedon alkaline development such as (meth)acrylate polymer, polynorbornene,cycloolefin-maleic anhydride copolymer, or ring-opening metathesispolymerization (ROMP) polymer. Also, the inventive polymer may beblended with a (meth)acrylate polymer having an acid labilegroup-substituted hydroxyl group wherein the exposed region is notdissolved by alkaline development, but a negative pattern is formed byorganic solvent development.

The resist composition used in the pattern forming process of theinvention may further comprise an organic solvent, a compound capable ofgenerating an acid in response to high-energy radiation (known as “acidgenerator”), and optionally, a dissolution regulator, basic compound,surfactant, acetylene alcohol, and other components.

The resist composition used herein may include an acid generator inorder for the composition to function as a chemically amplified positiveresist composition. Typical of the acid generator used herein is aphotoacid generator (PAG) capable of generating an acid in response toactinic light or radiation. The PAG may preferably be compounded in anamount of 0.5 to 30 parts and more preferably 1 to 20 parts by weightper 100 parts by weight of the base resin. The PAG is any compoundcapable of generating an acid upon exposure to high-energy radiation.Suitable PAGs include sulfonium salts, iodonium salts,sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acidgenerators. The PAGs may be used alone or in admixture of two or more.Typically acid generators generate such acids as sulfonic acids, imideacids and methide acids. Of these, sulfonic acids which are fluorinatedat α-position are most commonly used. In case the acid labile group isan acetal group which is susceptible to deprotection, the sulfonic acidneed not necessarily be fluorinated at α-position. Preferably, both anacid generator capable of generating a sulfonic acid fluorinated atα-position, imide acid or methide acid, and a sulfonate of a sulfonicacid non-fluorinated at α-position or an optionally fluorinatedcarboxylic acid are contained as the acid generator. In the embodimentwherein the base polymer has recurring units (e1), (e2) or (e3) of acidgenerator copolymerized therein, the acid generator need not beseparately added.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880).Specifically, exemplary solvents include ketones such as cyclohexanoneand methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate; and lactones such as γ-butyrolactone, and mixtures thereof.Where the acid labile group used is of acetal type, a high-boilingalcohol solvent may be added for accelerating deprotection reaction ofacetal, for example, diethylene glycol, propylene glycol, glycerol,1,4-butane diol, and 1,3-butane diol.

Exemplary basic compounds include primary, secondary and tertiary aminecompounds, specifically amine compounds having a hydroxyl, ether, ester,lactone, cyano or sulfonic acid ester group, as described in JP-A2008-111103, paragraphs [0146] to [0164], and compounds having acarbamate group, as described in JP 3790649.

Onium salts such as sulfonium salts, iodonium salts and ammonium saltsof sulfonic acids which are not fluorinated at α-position as describedin JP-A 2008-158339 and similar onium salts of carboxylic acids asdescribed in U.S. Pat. No. 6,136,500 (JP 3991462) and US 20080153030(JP-A 2008-158339) may be used as the quencher. While an α-positionfluorinated sulfonic acid, imide acid, and methide acid are necessary todeprotect the acid labile group of carboxylic acid ester, an α-positionnon-fluorinated sulfonic acid and a carboxylic acid are released by saltexchange with an onium salt which is not fluorinated at α-position. Anα-position non-fluorinated sulfonic acid and a carboxylic acid functionas a quencher because they do not induce deprotection reaction. Inaddition, an onium salt of α-position non-fluorinated sulfonic acid orcarboxylic acid undergoes a salt exchange with α-position fluorinatedsulfonic acid, imide acid or methide acid and converts to an acidgenerator of generating α-position fluorinated sulfonic acid, imide acidor methide acid. As the exposure dose increases, generation ofα-position fluorinated sulfonic acid, imide acid or methide acid andsalt exchange with sulfonium salt are infinitely repeated. The sitewhere sulfonic acid, imide acid or methide acid is generated at the endof exposure shifts from the site where the sulfonium salt of sulfonicacid, imide acid or methide acid is initially present. Since the cycleof photo-acid generation and salt exchange is repeated many times, theacid generation point is averaged, which leads to reduced edge roughnessof resist pattern after development.

Since sulfonium salts and iodonium salts of an α-positionnon-fluorinated sulfonic acid and a carboxylic acid arephoto-decomposable, those portions receiving a high light intensity arereduced in quenching capability and increased in the concentration ofα-position fluorinated sulfonic acid, imide acid, or methide acid. As aresult, the exposed portions are improved in contrast. When a negativetone pattern is formed using an organic solvent, the improvement in thecontrast of exposed portions leads to an improvement in therectangularity of negative pattern. Onium salts including sulfoniumsalts, iodonium salts and ammonium salts of α-position non-fluorinatedsulfonic acid and a carboxylic acid are highly effective in controllingthe diffusion of an α-position fluorinated sulfonic acid, imide acid andmethide acid. This is because the onium salt resulting from saltexchange is less mobile due to a higher molecular weight. In the eventthat a hole pattern is formed by negative development, since acid isgenerated in many regions, it is very important to control the diffusionof acid from the exposed area to the unexposed area. The addition ofonium salts including sulfonium salts, iodonium salts and ammonium saltsof an α-position non-fluorinated sulfonic acid and a carboxylic acid aswell as the carbamate compound capable of generating an amine compoundunder the action of acid is very important from the aspect ofcontrolling acid diffusion.

In case the acid labile group is an acetal group which is very sensitiveto acid, the acid for eliminating the protective group need notnecessarily be a sulfonic acid fluorinated at α-position, imide acid ormethide acid. Sometimes, deprotection reaction may take place even withα-position non-fluorinated sulfonic acid. In this case, an onium salt ofcarboxylic acid is preferably used as the quencher.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165] to [0166]. Exemplary dissolution regulators are described in JP-A2008-122932 (US 2008090172), paragraphs to [0178], and exemplaryacetylene alcohols in paragraphs [0179] to [0182].

Also a polymeric additive may be added for improving the waterrepellency on surface of a resist film as spin coated. This additive maybe used in the topcoatless immersion lithography. These additives have aspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue andare described in JP-A 2007-297590 and JP-A 2008-111103. The waterrepellency improver to be added to the resist should be soluble in theorganic solvent as the developer. The water repellency improver ofspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue iswell soluble in the developer. A polymer having an amino group or aminesalt copolymerized as recurring units may serve as the water repellentadditive and is effective for preventing evaporation of acid during PEBand avoiding any hole pattern opening failure after development. Anappropriate amount of the water repellency improver is 0.1 to 20 parts,preferably 0.5 to 10 parts by weight per 100 parts by weight of the baseresin.

Notably, an appropriate amount of the organic solvent is 100 to 10,000parts, preferably 300 to 8,000 parts by weight, and an appropriateamount of the basic compound is 0.0001 to 30 parts, preferably 0.001 to20 parts by weight, per 100 parts by weight of the base resin. Amountsof the dissolution inhibitor, surfactant, and acetylene alcohol used maybe determined as appropriate to meet a particular purpose of addition.

Process

As alluded previously, the pattern forming process of the inventioncomprises the steps of coating the positive resist composition definedabove onto a substrate, prebaking the resist composition to form aresist film, exposing a selected region of the resist film tohigh-energy radiation, baking (PEB), and developing the exposed resistfilm in an organic solvent-based developer so that the unexposed regionof film is dissolved and the exposed region of film is left, therebyforming a negative tone pattern such as a hole or trench pattern.

Now referring to the drawings, the pattern forming process of theinvention is illustrated in FIG. 1. First, the positive resistcomposition is coated on a substrate to form a resist film thereon.Specifically, a resist film 40 of a positive resist composition isformed on a processable substrate 20 disposed on a substrate 10 directlyor via an intermediate intervening layer 30 as shown in FIG. 1A. Theresist film preferably has a thickness of 10 to 1,000 nm and morepreferably 20 to 500 nm. Prior to exposure, the resist film is heated orprebaked, preferably at a temperature of 60 to 180° C., especially 70 to150° C. for a time of 10 to 300 seconds, especially 15 to 200 seconds.

The substrate 10 used herein is generally a silicon substrate. Theprocessable substrate (or target film) 20 used herein includes SiO₂,SiN, SiON, SiOC, p-Si, α-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi,low dielectric film, and etch stopper film. The intermediate interveninglayer 30 includes hard masks of SiO₂, SiN, SiON or p-Si, an undercoat inthe form of carbon film, a silicon-containing intermediate film, and anorganic antireflective coating.

Next comes exposure depicted at 50 in FIG. 1B. For the exposure,preference is given to high-energy radiation having a wavelength of 140to 250 nm, EUV having a wavelength of 13.5 nm, and electron beam (EB),and especially ArF excimer laser radiation of 193 nm wavelength. Theexposure may be done either in a dry atmosphere such as air or nitrogenstream or by immersion lithography in water. The ArF immersionlithography uses deionized water or liquids having a refractive index ofat least 1 and highly transparent to the exposure wavelength such asalkanes as the immersion solvent. The immersion lithography involvesexposing the prebaked resist film to light through a projection lens,with water introduced between the resist film and the projection lens.Since this allows lenses to be designed to a NA of 1.0 or higher,formation of finer feature size patterns is possible. The immersionlithography is important for the ArF lithography to survive to the 45-nmnode. In the case of immersion lithography, deionized water rinsing (orpost-soaking) may be carried out after exposure for removing waterdroplets left on the resist film, or a protective film may be appliedonto the resist film after pre-baking for preventing any leach-out fromthe resist film and improving water slip on the film surface.

The resist protective film used in the immersion lithography ispreferably formed from a solution of a polymer having1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble in water,but soluble in an alkaline developer, in a solvent selected fromalcohols of at least 4 carbon atoms, ethers of 8 to 12 carbon atoms, andmixtures thereof. The protective film-forming composition used hereinmay be based on a polymer comprising recurring units derived from amonomer having a 1,1,1,3,3,3-hexafluoro-2-propanol residue. While theprotective film must dissolve in the organic solvent developer, thepolymer comprising recurring units derived from a monomer having a1,1,1,3,3,3-hexafluoro-2-propanol residue dissolves in the organicsolvent developers. In particular, protective film-forming materialshaving 1,1,1,3,3,3-hexafluoro-2-propanol residues as described in JP-A2007-025634 and 2008-003569 readily dissolve in the organicsolvent-based developer.

In the protective film-forming composition, an amine compound or aminesalt may be added, or a polymer comprising recurring units containing anamino group or amine salt copolymerized therein may be used as the baseresin. This component is effective for controlling diffusion of the acidgenerated in the exposed region of the resist film to the unexposedregion for thereby preventing any hole opening failure. A usefulprotective film-forming composition having an amine compound addedthereto is described in JP-A 2008-003569. A useful protectivefilm-forming composition containing a polymer having an amino group oramine salt copolymerized therein is described in JP-A 2007-316448. Theamine compound or amine salt may be selected from the compoundsenumerated as the basic compound to be added to the resist composition.An appropriate amount of the amine compound or amine salt added is 0.01to 10 parts, preferably 0.02 to 8 parts by weight per 100 parts byweight of the base resin.

After formation of the resist film, deionized water rinsing (orpost-soaking) may be carried out for extracting the acid generator andother components from the film surface or washing away particles, orafter exposure, rinsing (or post-soaking) may be carried out forremoving water droplets left on the resist film. If the acid evaporatingfrom the exposed region during PEB deposits on the unexposed region todeprotect the protective group on the surface of the unexposed region,there is a possibility that the surface edges of holes after developmentare bridged to close the holes. Particularly in the case of negativedevelopment, regions surrounding the holes receive light so that acid isgenerated therein. There is a possibility that the holes are not openedif the acid outside the holes evaporates and deposits inside the holesduring PEB. Provision of a protective film is effective for preventingevaporation of acid and for avoiding any hole opening failure. Aprotective film having an amine compound or amine salt added thereto ismore effective for preventing acid evaporation. On the other hand, aprotective film formed of a composition comprising a polymer and anacidic compound having a carboxyl or sulfo group or a compositioncomprising a polymer having an acidic compound having a carboxyl orsulfo group copolymerized therein is not preferred because a holeopening failure can occur.

The other embodiment is a pattern forming process comprising the stepsof applying a resist composition comprising a polymer comprisingrecurring units of acid labile group-substituted vinyl alcohol andmaleic anhydride and/or maleimide, an acid generator, and an organicsolvent onto a substrate, prebaking the composition to form a resistfilm, forming a protective film on the resist film, exposing the resistfilm to high-energy radiation, typically by immersion lithography,baking, and applying an organic solvent-based developer to dissolve awaythe protective film and the unexposed region of resist film for forminga negative pattern wherein the exposed region of resist film is notdissolved. The protective film is preferably formed from a compositioncomprising a polymer bearing a 1,1,1,3,3,3-hexafluoro-2-propanol residueand an amino group or amine salt-containing compound, or a compositioncomprising a polymer comprising recurring units having a1,1,1,3,3,3-hexafluoro-2-propanol residue and recurring units having anamino group or amine salt copolymerized, the composition furthercomprising an alcohol solvent of at least 4 carbon atoms, an ethersolvent of 8 to 12 carbon atoms, or a mixture thereof.

Examples of suitable recurring units having a1,1,1,3,3,3-hexafluoro-2-propanol residue include those derived fromhydroxyl-bearing monomers selected from among the monomers listed onpages 52, 53 and 54. Examples of the amino group-containing compoundinclude the amine compounds described in JP-A 2008-111103, paragraphs[0146] to [0164] as being added to photoresist compositions. Examples ofthe amine salt-containing compound include salts of the foregoing aminecompounds with carboxylic acids or sulfonic acids.

Suitable alcohols of 4 or more carbon atoms include 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether solvents of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-t-amylether, and di-n-hexyl ether.

Exposure is preferably performed in an exposure dose of about 1 to 200mJ/cm², more preferably about 10 to 100 mJ/cm². This is followed bybaking (PEB) on a hot plate at 60 to 150° C. for 1 to 5 minutes,preferably at 80 to 120° C. for 1 to 3 minutes.

Thereafter the exposed resist film is developed in an organicsolvent-based developer for 0.1 to 3 minutes, preferably 0.5 to 2minutes by any conventional techniques such as dip, puddle and spraytechniques. In this way, the unexposed region of resist film isdissolved away, leaving a negative resist pattern 40 on the substrate 10as shown in FIG. 1C.

The organic solvent used as the developer is preferably selected fromamong ketones such as 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, and methylacetophenone; and esterssuch as propyl acetate, butyl acetate, isobutyl acetate, amyl acetate,isoamyl acetate, butenyl acetate, propyl formate, butyl formate,isobutyl formate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methylphenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate. These organic solvents may be used alone or inadmixture of two or more.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alkanes of 6 to 12 carbonatoms include hexane, heptane, octane, nonane, decane, undecane,dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-amylether, and di-n-hexyl ether. The solvents may be used alone or inadmixture. Besides the foregoing solvents, aromatic solvents may beused, for example, toluene, xylene, ethylbenzene, isopropylbenzene,tert-butylbenzene and mesitylene.

Where a hole pattern is formed by negative tone development, exposure bydouble dipole illuminations of X- and Y-direction line patterns providesthe highest contrast light. The contrast may be further increased bycombining dipole illumination with s-polarized illumination.

In a preferred embodiment, the exposure step is carried out byphotolithography, typically ArF immersion lithography, using a halftonephase shift mask bearing a lattice-like shifter pattern, whereby apattern of holes is formed at the intersections between gratings of thelattice-like shifter pattern after development. In a further preferredembodiment, the halftone phase shift mask bearing a lattice-like shifterpattern has a transmittance of 3 to 15%. In a further preferredembodiment, the phase shift mask used is a phase shift mask including alattice-like first shifter having a line width equal to or less than ahalf pitch and a second shifter arrayed on the first shifter andconsisting of lines whose on-wafer size is 2 to 30 nm thicker than theline width of the first shifter, whereby a pattern of holes is formedonly where the thick shifter is arrayed. In a further preferredembodiment, the phase shift mask used is a phase shift mask including alattice-like first shifter having a line width equal to or less than ahalf pitch and a second shifter arrayed on the first shifter andconsisting of dots whose on-wafer size is 2 to 100 nm thicker than theline width of the first shifter, whereby a pattern of holes is formedonly where the thick shifter is arrayed.

FIG. 2 is an optical image of X-direction lines having a pitch of 90 nmand a line size of 45 nm printed under conditions: ArF excimer laser ofwavelength 193 nm, NA 1.3 lens, dipole illumination, 6% halftone phaseshift mask, and s-polarization. FIG. 3 is an optical image ofY-direction lines having a pitch of 90 nm and a line size of 45 nmprinted under conditions: ArF excimer laser of wavelength 193 nm, NA 1.3lens, dipole illumination, 6% halftone phase shift mask, ands-polarization. A black area is a light shielded area while a white areais a high light intensity area. A definite contrast difference isrecognized between white and black, indicating the presence of a fullylight shielded area. FIG. 4 shows a contrast image obtained byoverlaying the optical image of X-direction lines in FIG. 2 with that ofY-direction lines in FIG. 3. Against the expectation that a combinationof X and Y lines may form a lattice-like image, weak light black areasdraw circular shapes. As the pattern (circle) size becomes larger, thecircular shape changes to a rhombic shape to merge with adjacent ones.As the circle size becomes smaller, circularity is improved, which isevidenced by the presence of a fully light shielded small circle.

Exposure by double dipole illuminations of X- and Y-direction linescombined with polarized illumination presents a method of forming lightof the highest contrast. This method, however, has the drawback that thethroughput is substantially reduced by double exposures and maskexchange therebetween. To continuously carry out two exposures whileexchanging a mask, the exposure tool must be equipped with two maskstages although the existing exposure tool includes a single mask stage.Higher throughputs may be obtained by carrying out exposure of Xdirection lines continuously on 25 wafers in a front-opening unified pod(FOUP), exchanging the mask, and carrying out exposure continuously onthe same 25 wafers, rather than exchanging a mask on every exposure of asingle wafer. However, a problem arises that as the time duration untilthe first one of 25 wafers is exposed in the second exposure isprolonged, the environment affects the resist such that the resist afterdevelopment may change its size and shape. To block the environmentalimpact on wafers in standby until the second exposure, it is effectivethat the resist film is overlaid with a protective film.

To proceed with a single mask, it is proposed in Non-Patent Document 1to carry out two exposures by dipole illuminations in X and Y directionsusing a mask bearing a lattice-like pattern. When this method iscompared with the above method using two masks, the optical contrast issomewhat reduced, but the throughput is improved by the use of a singlemask. As described in Non-Patent Document 1, the method involves formingX-direction lines in a first photoresist film by X-direction dipoleillumination using a mask bearing a lattice-like pattern, insolubilizingthe X-direction lines by light irradiation, coating a second photoresistfilm thereon, and forming Y-direction lines by Y-direction dipoleillumination, thereby forming holes at the interstices between X- andY-direction lines. Although only a single mask is needed, this methodincludes additional steps of insolubilizing the first photoresistpattern between the two exposures, and coating and developing the secondphotoresist film. Then the wafer must be removed from the exposure stagebetween the two exposures, giving rise to the problem of an increasedalignment error. To minimize the alignment error between two exposures,two exposures must be continuously carried out without removing thewafer from the exposure stage.

FIG. 18 shows the shape of apertures for dipole illumination for formingX-direction or horizontal lines using a mask bearing a lattice-likepattern, and FIG. 19 shows the shape of apertures for dipoleillumination for forming Y-direction or vertical lines. The addition ofs-polarized illumination to dipole illumination provides a furtherimproved contrast and is thus preferably employed. After two exposuresfor forming X- and Y-direction lines using a lattice-like mask areperformed in an overlapping manner, negative tone development isperformed to form a hole pattern.

When it is desired to form a hole pattern via a single exposure using alattice-like mask, a quadra-pole illumination or cross-pole illuminationin the aperture configuration shown in FIG. 20 is used. The contrast maybe improved by combining it with X—Y polarized illumination orazimuthally polarized illumination of circular polarization.

In the hole pattern forming process of the invention, when two exposuresare involved, these exposures are carried out by changing theillumination and mask for the second exposure from those for the firstexposure, whereby a fine size pattern can be formed at the highestcontrast and to dimensional uniformity. The masks used in the first andsecond exposures bear first and second patterns of intersecting lineswhereby a pattern of holes at intersections of lines is formed in theresist film after development. The first and second lines are preferablyat right angles although an angle of intersection other than 90° may beemployed. The first and second lines may have the same or different sizeand/or pitch. If a single mask bearing first lines in one area andsecond lines in a different area is used, it is possible to performfirst and second exposures continuously. In this case, however, themaximum area available for exposure is one half. Notably, the continuousexposures lead to a minimized alignment error. Of course, the singleexposure provides a smaller alignment error than the two continuousexposures.

When two exposures are performed using a single mask without reducingthe exposure area, the mask pattern may be a lattice-like pattern asshown in FIG. 5, a dot pattern as shown in FIG. 7, or a combination of adot pattern and a lattice-like pattern as shown in FIG. 11. The use of alattice-like pattern contributes to the most improved light contrast,but has the drawback of a reduced resist sensitivity due to a loweringof light intensity. On the other hand, the use of a dot pattern suffersa lowering of light contrast, but provides the merit of an improvedresist sensitivity.

Where holes are arrayed in horizontal and vertical directions, theabove-described illumination and mask pattern are used. Where holes arearrayed at a different angle, for example, at an angle of 45°, a mask ofa 45° arrayed pattern is combined with dipole illumination or cross-poleillumination.

Where two exposures are performed, a first exposure by a combination ofdipole illumination with polarized illumination for enhancing thecontrast of X-direction lines is followed by a second exposure by acombination of dipole illumination with polarized illumination forenhancing the contrast of Y-direction lines. Two continuous exposureswith the X- and Y-direction contrasts emphasized through a single maskcan be performed on a currently commercially available scanner.

The method of combining X and Y polarized illuminations with cross-poleillumination using a mask bearing a lattice-like pattern can form a holepattern through a single exposure, despite a slight lowering of lightcontrast as compared with two exposures of dipole illumination. Themethod is estimated to attain a substantial improvement in throughputand avoids the problem of misalignment between two exposures. Using sucha mask and illumination, a hole pattern of the order of 40 nm can beformed at a practically acceptable cost.

On use of a mask bearing a lattice-like pattern as shown in FIG. 5 wherelight is fully shielded at intersections between gratings, black spotshaving a very high degree of light shielding appear as shown in FIG. 6.FIG. 6 is an optical image of a lattice-like line pattern having a pitchof 90 nm and a line width of 30 nm printed under conditions: NA 1.3lens, cross-pole illumination, 6% halftone phase shift mask, andazimuthally polarized illumination. A fine hole pattern may be formed byperforming exposure through a mask bearing such a pattern and organicsolvent development entailing positive/negative reversal.

On use of a mask bearing a dot pattern of square dots having a pitch of90 nm and a side width of 55 nm as shown in FIG. 7, under conditions: NA1.3 lens, cross-pole illumination, 6% halftone phase shift mask, andazimuthally polarized illumination, an optical image is obtained asshown in FIG. 8 that depicts the contrast thereof. Although the circleof fully light shielded spot in FIG. 8 has a smaller area than in FIG.6, which indicates a low contrast as compared with the lattice-likepattern mask, the formation of a hole pattern is possible owing to thepresence of black or light shielded spots.

It is difficult to form a fine hole pattern that holes are randomlyarrayed at varying pitch and position. The super-resolution technologyusing off-axis illumination (such as dipole or cross-pole illumination)in combination with a phase shift mask and polarization is successful inimproving the contrast of dense (or grouped) patterns, but not so thecontrast of isolated patterns.

When the super-resolution technology is applied to repeating densepatterns, the pattern density bias between dense and isolated patterns,known as proximity bias, becomes a problem. As the super-resolutiontechnology used becomes stronger, the resolution of a dense pattern ismore improved, but the resolution of an isolated pattern remainsunchanged. Then the proximity bias is exaggerated. In particular, anincrease of proximity bias in a hole pattern resulting from furtherminiaturization poses a serious problem. One common approach taken tosuppress the proximity bias is by biasing the size of a mask pattern.Since the proximity bias varies with properties of a photoresistcomposition, specifically dissolution contrast and acid diffusion, theproximity bias of a mask varies with the type of photoresistcomposition. For a particular type of photoresist composition, a maskhaving a different proximity bias must be used. This adds to the burdenof mask manufacturing. Then the pack and unpack (PAU) method is proposedin Proc. SPIE Vol. 5753, p 171 (2005), which involves strongsuper-resolution illumination of a first positive resist to resolve adense hole pattern, coating the first positive resist pattern with anegative resist film material in alcohol solvent which does not dissolvethe first positive resist pattern, exposure and development of anunnecessary hole portion to close the corresponding holes, therebyforming both a dense pattern and an isolated pattern. One problem of thePAU method is misalignment between first and second exposures, as theauthors point out in the report. The hole pattern which is not closed bythe second development experiences two developments and thus undergoes asize change, which is another problem.

To form a random pitch hole pattern by organic solvent developmententailing positive/negative reversal, a mask is used in which alattice-like pattern is arrayed over the entire surface and the width ofgratings is thickened only where holes are to be formed. As shown inFIG. 9, on a lattice-like pattern having a pitch of 90 nm and a linewidth of 20 nm, thick crisscross or intersecting line segments aredisposed where dots are to be formed. A black area corresponds to thehalftone shifter portion. Line segments with a width of 30 nm aredisposed in the dense pattern portion whereas thicker line segments(width 40 nm in FIG. 9) are disposed in more isolated pattern portions.Since the isolated pattern provides light with a lower intensity thanthe dense pattern, thicker line segments are used. Since the peripheralarea of the dense pattern provides light with a relatively lowintensity, line segments having a width of 32 nm are assigned to theperipheral area which width is slightly greater than that in theinternal area of the dense pattern. FIG. 10 shows an optical image fromthe mask of FIG. 9, indicating the contrast thereof. Black or lightshielded areas are where holes are formed via positive/negativereversal. Black spots are found at positions other than where holes areformed, but few are transferred in practice because they are of smallsize. Optimization such as reduction of the width of grating linescorresponding to unnecessary holes can inhibit transfer of unnecessaryholes.

Also useful is a mask in which a lattice-like pattern is arrayed overthe entire surface and thick dots are disposed only where holes are tobe formed. As shown in FIG. 11, on a lattice-like pattern having a pitchof 90 nm and a line width of 15 nm, thick dots are disposed where dotsare to be formed. A black area corresponds to the halftone shifterportion. Square dots having one side with a size of 55 nm are disposedin the dense pattern portion whereas larger square dots (side size 90 nmin FIG. 11) are disposed in more isolated pattern portions. Althoughsquare dots are shown in the figure, the dots may have any shapeincluding rectangular, rhombic, pentagonal, hexagonal, heptagonal,octagonal, and polygonal shapes and even circular shape.

FIG. 12 shows an optical image from the mask of FIG. 11, indicating thecontrast thereof. The presence of black or light shielded spotssubstantially equivalent to those of FIG. 10 indicates that holes areformed via positive/negative reversal.

On use of a mask bearing no lattice-like pattern arrayed as shown inFIG. 13, black or light shielded spots do not appear as shown in FIG.14. In this case, holes are difficult to form, or even if holes areformed, a variation of mask size is largely reflected by a variation ofhole size because the optical image has a low contrast.

After development, a process for shrinking a hole pattern or trenchpattern may be carried out. Suitable shrink processes include thethermal flow process of heating the pattern as developed to inducethermal flow thereto for shrinkage, and the RELACS® process of coating ashrink agent onto the pattern as developed, baking and stripping theextra shrink agent while leaving the shrink agent bonded to the patternsurface.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight. For allpolymers, Mw and Mn are determined by GPC versus polystyrene standardsusing tetrahydrofuran solvent. For measurement of the hole size of apattern, a top-down scanning electron microscope (TDSEM) S-9380 (HitachiHigh Technologies Corp.) was used.

SYNTHESIS EXAMPLE

Various polymers (Resist Polymers 1 to 15, Comparative Resist Polymer 1,and Blending Resist Polymers 1, 2) for use in resist compositions wereprepared by combining suitable monomers, effecting copolymerizationreaction in tetrahydrofuran solvent, pouring into methanol forcrystallization, repeatedly washing with hexane, isolation, and drying.The polymers were analyzed by ¹H-NMR to determine their composition andby GPC to determine Mw and dispersity Mw/Mn.

Preparation of Positive Resist Composition and Alkali-Soluble ProtectiveFilm-Forming Composition

A resist composition in solution form was prepared by dissolving apolymer (Resist Polymer) and components in solvents in accordance withthe formulation of Table 1. A protective film-forming composition insolution form was prepared by dissolving a polymer (TC Polymer) andadditive in solvents in accordance with the formulation of Table 2. Thesolutions were filtered through a Teflon® filter with a pore size of 0.2μm. The components used herein are identified below.

Acid generator: PAG1 to PAG7 of the following structural formulae

Basic Compound: Quenchers 1 to 8 of the following structural formulae

Organic Solvent:

-   -   PGMEA (propylene glycol monomethyl ether acetate)    -   CyH (cyclohexanone)

TABLE 1 Acid Basic Organic Polymer generator compound Additive solvent(pbw) (pbw) (pbw) (pbw) (pbw) Resist 1 Resist PAG 1 Quencher — PGMEAPolymer 1 (10.0) 1 (2,000) (100) (1.50) CyH(500) Resist 2 Resist PAG 1Quencher Water- PGMEA Polymer 2 (5.0) 2 repellent (2,000) (100) (4.50)polymer 1 (3) CyH(500) Resist 3 Resist PAG 1 Quencher Water- PGMEAPolymer 3 (5.0) 3 repellent (2,000) (100) (4.50) polymer 1 (3) CyH(500)Resist 4 Resist PAG 3 Quencher Water- PGMEA Polymer 4 (10.0) 1 repellent(2,000) (100) (1.50) polymer 1 (3) CyH(500) Resist 5 Resist PAG 4Quencher Water- PGMEA Polymer 5 (9.0) 1 repellent (2,000) (100) (1.50)polymer 1 (3) CyH(500) Resist 6 Resist PAG 2 Quencher Water- PGMEAPolymer 6 (4.5) 4 repellent (2,000) (100) (4.50) polymer 1 (3) CyH(500)Resist 7 Resist PAG 1 Quencher Water- PGMEA Polymer 7 (10.0) 1 repellent(2,000) (100) (1.50) polymer 1 (3) CyH(500) Resist 8 Resist PAG 1Quencher Water- PGMEA Polymer 8 (10.0) 5 repellent (2,000) (100) (4.50)polymer 1 (3) CyH(500) Resist 9 Resist PAG 1 Quencher Water- PGMEAPolymer 9 (10.0) 6 repellent (2,000) (100) (4.50) polymer 1 (3) CyH(500)Resist Resist — Quencher Water- PGMEA 10 Polymer 10 5 repellent (2,000)(100) (4.50) polymer 1 (3) CyH(500) Resist Resist PAG 5 Quencher Water-PGMEA 11 Polymer 9 (6.5) 6 repellent (2,000) (100) (3.50) polymer 1 (3)CyH(500) Resist Resist PAG 5 Quencher Water- PGMEA 12 Polymer 9 (6.5) 7repellent (2,000) (100) (3.50) polymer 1 (3) CyH(500) Resist Resist PAG6 Quencher Water- PGMEA 13 Polymer 8 (5.5) 5 repellent (2,000) (100)(3.50) polymer 1 (3) CyH(500) Resist Resist PAG 7 Quencher Water- PGMEA14 Polymer 9 (5.5) 6 repellent (2,000) (100) (3.50) polymer 1 (3)CyH(500) Resist Resist PAG 7 Quencher Water- PGMEA 15 Polymer 11 (5.5) 6repellent (2,000) (100) (3.50) polymer 1 (3) CyH(500) Resist Resist PAG1 Quencher Water- PGMEA 16 Polymer 5 (10.0) 1 repellent (2,000) (50)(1.50) polymer 1 CyH(500) Blending (3) Resist Polymer 1 (50) ResistResist PAG 1 Quencher Water- PGMEA 17 Polymer 5 (10.0) 1 repellent(2,000) (50) (1.50) polymer 1 CyH(500) Blending (3) Resist Polymer 2(50) Resist Resist PAG 1 Quencher Water- PGMEA 18 Polymer 5 (10.0) 1repellent (2,000) (50) (1.50) polymer 1 CyH(500) Comparative (3) ResistPolymer 1 (50) Resist Resist PAG 7 Quencher Water- PGMEA 19 Polymer 4(4.5) 4 repellent (2,000) (50) (3.50) polymer 1 CyH(500) Resist (3)Polymer 8 (50) Resist Resist PAG 7 Quencher Water- PGMEA 20 Polymer 12(5.5) 6 repellent (2,000) (100) (3.50) polymer 1 (3) CyH(500) ResistResist PAG 7 Quencher Water- PGMEA 21 Polymer 13 (5.5) 6 repellent(2,000) (100) (3.50) polymer 1 (3) CyH(500) Resist Resist PAG 7 QuencherWater- PGMEA 22 Polymer 14 (5.5) 6 repellent (2,000) (100) (3.50)polymer 1 (3) CyH(500) Resist Resist PAG 7 Quencher Water- PGMEA 23Polymer 15 (5.5) 8 repellent (2,000) (100) (3.50) polymer 1 (3) CyH(500)Compar- Comparative PAG 1 Quencher Water- PGMEA ative Resist (10.0) 1repellent (2,000) Resist 1 Polymer 1 (1.50) polymer 1 (3) CyH(500) (100)

TABLE 2 Protective Polymer Additive Solvent Film (pbw) (pbw) (pbw) TC-1TC Polymer 1 tri-n-octylamine diisoamyl ether (100) (0.2) (2,400)2-methyl-1-butanol (240)

EXAMPLES AND COMPARATIVE EXAMPLES ArF Lithography Patterning Test 1

On a substrate (silicon wafer) having an antireflective coating ARC-29A(Nissan Chemical Industries, Ltd.) of 80 nm thick, the resistcomposition in Table 3 was spin coated and baked on a hot plate at 100°C. for 60 seconds to form a resist film of 100 nm thick.

Using an ArF excimer laser scanner NSR-305B (Nikon Corp., NA 0.68, σ0.73), the resist film was open-frame exposed while the dose was variedstepwise in an increment of 0.2 mJ/cm². The exposed resist film wasbaked (PEB) at 90° C. for 60 seconds and puddle developed for 30 secondsin the organic solvent shown in Table 1 as developer. The wafer wasrinsed at 500 rpm with 4-methyl-2-pentanol, spin dried at 2,000 rpm, andbaked at 100° C. for 60 seconds to evaporate off the rinse liquid.Separately, the same process was repeated until the PEB, and followed bydevelopment in a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueoussolution. The film thickness after PEB, the film thickness after organicsolvent development, and the film thickness after TMAH aqueous solutiondevelopment were measured. A contrast curve was determined by plottingthe film thickness versus the exposure dose. A residual film thicknessin the exposed region after development and a gradient (γ) weredetermined.

The contrast curves are shown in the diagrams of FIG. 15 (Example 1-1)and FIG. 16 (Comparative Example 1-1) wherein the dose is on abscissaand the film thickness is on ordinate. The film thickness loss andgradient (γ) are reported in Table 3. It is evident that the resistcomposition within the scope of the invention is characterized by aminimized film thickness loss during organic solvent development and ahigh contrast (γ).

TABLE 3 Film thickness loss of exposed region after Resist development(nm) γ Example 1-1 Resist 2 3.0 15.0 Comparative Comparative 5.8 8.75Example 1-1 Resist 1

ArF Lithography Patterning Test 2

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 4 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 100 nm thick. In someExamples, the protective film-forming composition shown in Table 2 wasspin coated on the resist film and baked at 90° C. for 60 seconds toform a protective film (or topcoat TC-1) of 50 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, σ 0.98/0.78, cross-pole opening 20 deg., azimuthallypolarized illumination), exposure was performed in a varying dosethrough a 6% halftone phase shift mask bearing a lattice-like patternwith a pitch of 90 nm and a line width of 30 nm (on-wafer size) whoselayout is shown in FIG. 17. After the exposure, the wafer was baked(PEB) at the temperature shown in Table 4 for 60 seconds and developed.Specifically, butyl acetate was injected from a development nozzle whilethe wafer was spun at 30 rpm for 3 seconds, which was followed bystationary puddle development for 27 seconds. The wafer was rinsed withdiisoamyl ether, spin dried, and baked at 100° C. for 20 seconds toevaporate off the rinse liquid.

A hole pattern resulted from image reversal by solvent development. Byobservation under TDSEM S-9380, the size of 50 holes was measured, fromwhich a size variation 3a was determined. The cross-sectional profile ofthe hole pattern was observed under electron microscope S-4300 (HitachiHigh Technologies Corp.). The results are shown in Table 4. It isevident that the resist compositions within the scope of the inventionform patterns having dimensional uniformity and a perpendicular profileafter organic solvent development.

TABLE 4 PEB Hole size temp. Dose variation 3σ Cross-sectional ResistProtective film (° C.) (mJ/cm²) (nm) profile Example 2-1 Resist 1  TC-1100 49 2.9 perpendicular Example 2-2 Resist 2  — 100 46 2.4perpendicular Example 2-3 Resist 3  — 90 43 2.5 perpendicular Example2-4 Resist 4  — 90 46 2.6 perpendicular Example 2-5 Resist 5  — 95 532.6 perpendicular Example 2-6 Resist 6  — 90 46 2.5 perpendicularExample 2-7 Resist 7  — 90 43 2.8 perpendicular Example 2-8 Resist 8  —95 40 2.6 perpendicular Example 2-9 Resist 9  — 90 43 2.6 perpendicularExample 2-10 Resist 10 — 100 44 2.3 perpendicular Example 2-11 Resist 11— 100 48 2.2 perpendicular Example 2-12 Resist 12 — 100 44 2.4perpendicular Example 2-13 Resist 13 — 95 49 2.5 perpendicular Example2-14 Resist 14 — 95 41 2.6 perpendicular Example 2-15 Resist 15 — 95 382.3 perpendicular Example 2-16 Resist 16 — 95 47 2.8 perpendicularExample 2-17 Resist 17 — 95 45 2.7 perpendicular Example 2-18 Resist 18— 95 44 2.7 perpendicular Example 2-19 Resist 19 — 95 43 2.3perpendicular Example 2-20 Resist 20 — 100 49 2.6 perpendicular Example2-21 Resist 21 — 100 47 2.7 perpendicular Example 2-22 Resist 22 — 10048 2.5 perpendicular Example 2-23 Resist 23 — 100 42 2.6 perpendicularComparative Comparative — 90 55 3.3 inversely Example 2-1 Resist 1tapered

ArF Lithography Patterning Test 3

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 5 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 100 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, σ 0.98/0.78, cross-pole opening 20 deg., azimuthallypolarized illumination), exposure was performed through a 6% halftonephase shift mask bearing a square dot pattern with a pitch of 90 nm anda side width of 55 nm (on-wafer size) whose layout is shown in FIG. 7,while the dose was varied. After the exposure, the wafer was baked (PEB)at the temperature shown in Table 5 for 60 seconds and developed.Specifically, methyl benzoate was injected from a development nozzlewhile the wafer was spun at 30 rpm for 3 seconds, which was followed bystationary puddle development for 27 seconds. The wafer was rinsed withxylene, spin dried, and baked at 100° C. for 20 seconds to evaporate offthe rinse liquid.

A hole pattern resulted from image reversal by solvent development. Byobservation under TDSEM S-9380, the size of holes was measured, fromwhich a focus margin affording a size of 40 nm±5 nm was determined asDOF. The size of 50 holes within a shot of the same dose and the samefocus was measured, from which a size variation 3σ was determined. Theresults are shown in Table 5.

TABLE 5 PEB Hole size temper- variation ature Dose DOF 3σ Resist (° C.)(mJ/cm²) (nm) (nm) Example 3-1 Resist 2 100 28 90 3.8 Example 3-2 Resist7 90 28 100 3.6 Comparative Comparative 90 31 85 4.0 Example 3-1 Resist1

ArF Lithography Patterning Test 4

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 6 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 100 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, σ 0.98/0.78, dipole opening 20 deg., azimuthallypolarized illumination), exposure was performed through a 6% halftonephase shift mask bearing a dot pattern with a pitch of 90 nm and a widthof 55 nm (on-wafer size) whose layout is shown in FIG. 7, while the dosewas varied. The same area was subjected to two continuous exposures by Xand Y dipole illuminations. After the exposure, the wafer was baked(PEB) at the temperature shown in Table 6 for 60 seconds and developed.Specifically, 2-heptanone was injected from a development nozzle whilethe wafer was spun at 30 rpm for 3 seconds, which was followed bystationary puddle development for 27 seconds. The wafer was rinsed withdiisoamyl ether, spin dried, and baked at 100° C. for 20 seconds toevaporate off the rinse liquid.

A hole pattern resulted from image reversal by solvent development. Byobservation under TDSEM S-9380, the size of holes was measured, fromwhich a focus margin affording a size of 40 nm±5 nm was determined asDOF. The size of 50 holes within a shot of the same dose and the samefocus was measured, from which a size variation 3σ was determined. Theresults are shown in Table 6.

TABLE 6 PEB Hole size temper- variation ature Dose DOF 3σ Resist (° C.)(mJ/cm²) (nm) (nm) Example 4-1 Resist 2 100 21 100 2.3 Example 4-2Resist 7 90 20 105 2.3 Comparative Comparative 90 22 90 3.4 Example 4-1Resist 1

ArF Lithography Patterning Test 5

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 7 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 100 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, σ 0.98/0.78, dipole opening 20 deg., azimuthallypolarized illumination), first exposure was performed through a 6%halftone phase shift mask bearing an array of X-direction lines with apitch of 80 nm and a line width of 40 nm (on-wafer size) by compliantdipole illumination. Next, second exposure was performed through a 6%halftone phase shift mask bearing an array of Y-direction lines with apitch of 80 nm and a line width of 40 nm (on-wafer size) by compliantdipole illumination. After the exposure, the wafer was baked (PEB) atthe temperature shown in Table 7 for 60 seconds and developed.Specifically, butyl acetate was injected from a development nozzle whilethe wafer was spun at 30 rpm for 3 seconds, which was followed bystationary puddle development for 27 seconds. The wafer was rinsed withdiisoamyl ether, spin dried, and baked at 100° C. for 20 seconds toevaporate off the rinse liquid.

A hole pattern resulted from image reversal by solvent development. Byobservation under TDSEM S-9380, the size of 50 holes was measured, fromwhich a size variation 3a was determined. The results are shown in Table7.

TABLE 7 PEB Hole size temperature Dose variation Resist (° C.) (mJ/cm²)3σ (nm) Example 5-1 Resist 2 100 21 2.0 Example 5-2 Resist 7 90 22 1.7Comparative Comparative 90 26 2.4 Example 5-1 Resist 1

ArF Lithography Patterning Test 6

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 8 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 100 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, σ 0.98/0.78, dipole opening 20 deg., azimuthallypolarized illumination), exposure was performed through a 6% halftonephase shift mask bearing a dot pattern with a pitch of 90 nm and a widthof 55 nm (on-wafer size) whose layout is shown in FIG. 7, while the dosewas varied. The same area was subjected to two continuous exposures by Xand Y dipole illuminations. After the exposure, the wafer was baked(PEB) at the temperature shown in Table 8 for 60 seconds and developed.Specifically, the solvent shown in Table 8 was injected from adevelopment nozzle while the wafer was spun at 30 rpm for 3 seconds,which was followed by stationary puddle development for 27 seconds. Thewafer was rinsed with diisoamyl ether, spin dried, and baked at 100° C.for 20 seconds to evaporate off the rinse liquid.

A hole pattern resulted from image reversal by solvent development. Byobservation under TDSEM S-9380, the size of holes was measured, fromwhich a focus margin affording a size of 40 nm±5 nm was determined asDOF. The size of 50 holes within a shot of the same dose and the samefocus was measured, from which a size variation 3σ was determined. Theresults are shown in Table 8.

TABLE 8 PEB Hole size temp. Dose DOF variation 3σ Resist (° C.) (mJ/cm²)Developer (nm) (nm) Example 6-1 Resist 7 90 28 2-heptanone 100 2.2Example 6-2 Resist 7 90 27 methyl benzoate 105 2.3 Example 6-3 Resist 790 28 ethyl benzoate 100 2.4 Example 6-4 Resist 7 90 29 phenyl acetate100 2.6 Example 6-5 Resist 7 90 32 benzyl acetate 100 2.5 Example 6-6Resist 7 90 23 methyl phenylacetate 100 2.6 Example 6-7 Resist 7 90 30methyl benzoate: 100 2.7 butyl acetate = 6:4 Example 6-8 Resist 7 90 28methyl benzoate: 100 2.6 2-heptanone = 5:5 Example 6-9 Resist 7 90 26ethyl 3-ethoxypropionate 100 2.7

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

Japanese Patent Application No. 2011-202930 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A pattern forming process, comprising:applying a resist composition onto a substrate, the resist compositioncomprising a polymer comprising recurring units of acid labilegroup-substituted vinyl alcohol and maleic anhydride and/or maleimide,an acid generator, and an organic solvent, prebaking the composition toform a resist film, exposing the resist film to high-energy radiation,baking, and developing the exposed film in an organic solvent-baseddeveloper to form a negative pattern wherein the unexposed region offilm is dissolved away and the exposed region of film is not dissolved,wherein the recurring units of acid labile group-substituted vinylalcohol and maleic anhydride and/or maleimide are represented by thegeneral formula (1):

wherein R¹ is an acid labile group, wherein X is an oxygen atom or NR²,wherein R² is hydrogen, hydroxyl, or a straight, branched or cyclicC₁-C₆ alkyl group which may contain one or two or more groups selectedfrom the group consisting of hydroxyl, ether, ester, carbonyl, andacid-labile groups, wherein a1 and a2 are numbers in the range:0<a1<1.0, 0<a2<1.0, and 0<a1+a2≦1.0, wherein said acid labile group isselected from groups of the formula (AL-10) and acetal groups of theformula (AL-11):

wherein R⁵¹ and R⁵⁴ each are a monovalent hydrocarbon group of 1 to 40carbon atoms which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine; wherein R⁵² and R⁵³ each are hydrogen or amonovalent hydrocarbon group of 1 to 20 carbon atoms which may contain aheteroatom such as oxygen, sulfur, nitrogen or fluorine; wherein a5 isan integer of 0 to 10; and wherein a pair of R⁵² and R⁵³, R⁵² and R⁵⁴ orR⁵³ and R⁵⁴ may bond together to form a ring with the carbon atom or thecarbon and oxygen atoms to which they are attached, the ring having 3 to20 carbon atoms.
 2. The pattern forming process according to claim 1,further comprising forming a protective film on the resist film, afterprebaking and prior to exposing, wherein the developing includesdissolving away the protective film.
 3. The process of claim 1, whereinthe acid generator comprises an acid generator capable of generating asulfonic acid fluorinated at alpha-position, imide acid or methide acid,and a sulfonate of a sulfonic acid non-fluorinated at alpha-position oran optionally fluorinated carboxylic acid.
 4. The process of claim 1,wherein the developer comprises at least one organic solvent selectedfrom the group consisting of 2-octanone, 2-nonanone, 2-heptanone,3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, phenyl acetate, propyl formate, butyl formate, isobutylformate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate.
 5. Theprocess of claim 1, wherein the step of exposing the resist film tohigh-energy radiation includes ArF excimer laser lithography of 193 nmwavelength, EUV lithography of 13.5 nm wavelength or EB lithography. 6.The process of claim 5, wherein the ArF lithography of 193 nm wavelengthuses a halftone phase shift mask bearing a dot shifter pattern, wherebya pattern of holes is formed at the dots after development.
 7. Theprocess of claim 1, wherein the exposure step uses halftone phase shiftmasks and includes two exposures of two intersecting sets of lines,whereby a pattern of holes is formed at the intersections between linesafter development.
 8. The process of claim 1, wherein the exposure stepuses a halftone phase shift mask bearing lattice-like shifter gratings,whereby a pattern of holes is formed at the intersections of gratingsafter development.
 9. The process of claim 1, wherein X is NR².
 10. Apattern forming process, comprising: applying a resist composition ontoa substrate, the resist composition comprising a polymer comprisingrecurring units of acid labile group-substituted vinyl alcohol andmaleic anhydride and/or maleimide, and recurring units of at least onetype selected from sulfonium salts (e1) to (e3) of the following generalformula, and

an organic solvent, prebaking the composition to form a resist film,exposing the resist film to high-energy radiation, baking, anddeveloping the exposed film in an organic solvent-based developer toform a negative pattern wherein the unexposed region of film isdissolved away and the exposed region of film is not dissolved, whereinR²⁰, R²⁴ and R²⁸ each are hydrogen or methyl, wherein R²¹ is a singlebond, phenylene, —O—R³³—, or —C(═O)—Y—R³³—, wherein Y is oxygen or NH,wherein R³³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene group or phenylene group, which may contain a carbonyl(—CO—), ester (—COO—), ether (—O—) or hydroxyl radical, wherein R²²,R²³, R²⁵, R²⁶, R²⁷, R²⁹, R³⁰, and R³¹ are each independently a straight,branched or cyclic C₁-C₁₂ alkyl group which may contain a carbonyl,ester or ether radical, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenylgroup, wherein Z₀ is a single bond, methylene, ethylene, phenylene,fluorophenylene, —O—R³²—, or —C(═O)—Z₁—R³²—, wherein Z₁ is oxygen or NH,wherein R³² is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene group or phenylene group, which may contain a carbonyl,ester, ether or hydroxyl radical, wherein M⁻ is a non-nucleophiliccounter ion, wherein e1, e2 and e3 are numbers in the range: 0≦e1≦0.3,0≦e2≦0.3, 0≦e3≦0.3, and 0<e1+e2+e3≦0.3, wherein an acid generator is notincluded, wherein the recurring units of acid labile group-substitutedvinyl alcohol and maleic anhydride and/or maleimide are represented bythe general formula (I):

wherein R¹ is an acid labile group, wherein X is an oxygen atom or NR²,wherein R² is hydrogen, hydroxyl, or a straight, branched or cyclicC₁-C₆ alkyl group which may contain one or two or more groups selectedfrom the group consisting of hydroxyl, ether, ester, carbonyl, andacid-labile groups, wherein a1 and a2 are numbers in the range:0<a1<1.0, 0<a2<1.0, and 0<a1+a2≦1.0. wherein said acid labile group isselected from groups of the formula (AL-10) and acetal groups of theformula (AL-11):

wherein R⁵¹ and R⁵⁴ each are a monovalent hydrocarbon group of 1 to 40carbon atoms which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine; wherein R⁵² and R⁵³ each are hydrogen or amonovalent hydrocarbon group of 1 to 20 carbon atoms which may contain aheteroatom such as oxygen, sulfur, nitrogen or fluorine; wherein a5 isan integer of 0 to 10; and wherein a pair of R⁵² and R⁵³, R⁵² and R⁵⁴ orR⁵³ and R⁵⁴ may bond together to form a ring with the carbon atom or thecarbon and oxygen atoms to which they are attached, the ring having 3 to20 carbon atoms.
 11. A negative pattern-forming resist composition,comprising: a polymer comprising recurring units (a1) of acid labilegroup-substituted vinyl alcohol and recurring units (a2) of maleicanhydride and/or maleimide, represented by the general formula (I), anacid generator, and an organic solvent,

wherein R¹ is an acid labile group, wherein X is an oxygen atom or NR²,wherein R² is hydrogen, hydroxyl, or a straight, branched or cyclicC₁-C₆ alkyl group which may contain one or two or more groups selectedfrom the group consisting of hydroxyl, ether, ester, carbonyl, andacid-labile groups, wherein a1 and a2 are numbers in the range:0<a1<1.0, 0<a2<1.0, and 0<a1+a2≦1.0, wherein when said negativepattern-forming resist composition is cured, an unexposed region of saida cured resist composition is dissolved away and an exposed region ofsaid cured resist composition is not dissolved in a developer selectedfrom the group consisting of 2-octanone, 2-nonanone, 2-heptanone,3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, phenyl acetate, propyl formate, butyl formate, isobutylformate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate, wherein saidacid labile group is selected from groups of the formula (AL-10) andacetal groups of the formula (AL-11):

wherein R⁵¹ and R⁵⁴ each are a monovalent hydrocarbon group of 1 to 40carbon atoms which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine; wherein R⁵² and R⁵³ each are hydrogen or amonovalent hydrocarbon group of 1 to 20 carbon atoms which may contain aheteroatom such as oxygen, sulfur, nitrogen or fluorine; wherein a5 isan integer of 0 to 10; and wherein a pair of R⁵² and R⁵³, R⁵² and R⁵⁴ orR⁵³ and R⁵⁴ may bond together to form a ring with the carbon atom or thecarbon and oxygen atoms to which they are attached, the ring having 3 to20 carbon atoms.
 12. A negative pattern-forming resist composition,comprising: a polymer comprising recurring units (a1) of acid labilegroup-substituted vinyl alcohol and recurring units (a2) of maleicanhydride and/or maleimide, represented by the general formula (1), andrecurring units of at least one type selected from sulfonium salts (e1)to (e3) of the following general formula, and

an organic solvent, wherein R¹ is an acid labile group, wherein X is anoxygen atom or NR², wherein R² is hydrogen, hydroxyl, or a straight,branched or cyclic C₁-C₆ alkyl group which may contain one or two ormore groups selected from the group consisting of hydroxyl, ether,ester, carbonyl, and acid-labile groups, wherein a1 and a2 are numbersin the range: 0<a1<1.0, 0<a2<1.0, and 0<a1+a2≦1.0, wherein when saidnegative pattern-forming resist composition is cured, an unexposedregion of a cured resist composition is dissolved away and an exposedregion of said cured resist composition is not dissolved in a developerselected from the group consisting of 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,amyl acetate, isoamyl acetate, butenyl acetate, phenyl acetate, propylformate, butyl formate, isobutyl formate, amyl formate, isoamyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,amyl lactate, isoamyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, benzyl acetate,methyl phenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate, wherein R²⁰, R²⁴ and R²⁸ each are hydrogen ormethyl, wherein R²¹ is a single bond, phenylene, —O—R³³—, or—C(═O)—Y—R³³—, wherein Y is oxygen or NH, wherein R³³ is a straight,branched or cyclic C₁-C₆ alkylene group, alkenylene group or phenylenegroup, which may contain a carbonyl (—CO—), ester (—COO—), ether (—O—)or hydroxyl radical, wherein R²², R²³, R²⁵, R²⁶, R²⁷, R²⁹, R³⁰ and R³¹are each independently a straight, branched or cyclic C₁-C₁₂ alkyl groupwhich may contain a carbonyl, ester or ether radical, or a C₆-C₁₂ aryl,C₇-C₂₀ aralkyl, or thiophenyl group, wherein Z₀ is a single bond,methylene, ethylene, phenylene, fluorophenylene, —O—R³²—, or—C(═O)—Z₁—R³²—, wherein Z₁ is oxygen or NH, wherein R³² is a straight,branched or cyclic C₁-C₆ alkylene group, alkenylene group or phenylenegroup, which may contain a carbonyl, ester, ether or hydroxyl radical,wherein M⁻ is a non-nucleophilic counter ion, wherein e1, e2 and e3 arenumbers in the range: 0≦e1≦0.3, 0≦e2≦0.3, 0≦e3≦0.3, and 0<e1+e2+e3≦0.3,wherein an acid generator is not included, wherein said acid labilegroup is selected from groups of the formula (AL-10) and acetal groupsof the formula (AL-11):

wherein R⁵¹ and R⁵⁴ each are a monovalent hydrocarbon group of 1 to 40carbon atoms which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine; wherein R⁵² and R⁵³ each are hydrogen or amonovalent hydrocarbon group of 1 to 20 carbon atoms which may contain aheteroatom such as oxygen, sulfur, nitrogen or fluorine; wherein a5 isan integer of 0 to 10; and wherein a pair of R⁵² and R⁵³, R⁵² and R⁵⁴ orR⁵³ and R⁵⁴ may bond together to form a ring with the carbon atom or thecarbon and oxygen atoms to which they are attached, the ring having 3 to20 carbon atoms.
 13. The resist composition of claim 11, wherein theacid generator comprises an acid generator capable of generating asulfonic acid fluorinated at alpha-position, imide acid or methide acid,and a sulfonate of a sulfonic acid non-fluorinated at alpha-position oran optionally fluorinated carboxylic acid.
 14. The resist composition ofclaim 11, wherein X is NR².